source: mainline/kernel/arch/arm32/src/userspace.c@ 3bacee1

/*
 * Copyright (c) 2007 Petr Stepan, Pavel Jancik
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/** @addtogroup arm32
 * @{
 */
/** @file
 *  @brief Userspace switch.
 */

#include <stdbool.h>
#include <userspace.h>
#include <arch/ras.h>

/** Struct for holding all general purpose registers.
 *
 *  Used to set registers when going to userspace.
 */
typedef struct {
        uint32_t r0;
        uint32_t r1;
        uint32_t r2;
        uint32_t r3;
        uint32_t r4;
        uint32_t r5;
        uint32_t r6;
        uint32_t r7;
        uint32_t r8;
        uint32_t r9;
        uint32_t r10;
        uint32_t r11;
        uint32_t r12;
        uint32_t sp;
        uint32_t lr;
        uint32_t pc;
} ustate_t;

/** Change processor mode
 *
 * @param kernel_uarg Userspace settings (entry point, stack, ...).
 *
 */
void userspace(uspace_arg_t *kernel_uarg)
{
        volatile ustate_t ustate;

        /* set first parameter */
        ustate.r0 = (uintptr_t) kernel_uarg->uspace_uarg;

        /* %r1 is defined to hold pcb_ptr - set it to 0 */
        ustate.r1 = 0;

        /* pass the RAS page address in %r2 */
        ustate.r2 = (uintptr_t) ras_page;

        /* clear other registers */
        ustate.r3 = 0;
        ustate.r4 = 0;
        ustate.r5 = 0;
        ustate.r6 = 0;
        ustate.r7 = 0;
        ustate.r8 = 0;
        ustate.r9 = 0;
        ustate.r10 = 0;
        ustate.r11 = 0;
        ustate.r12 = 0;
        ustate.lr = 0;

        /* set user stack */
        ustate.sp = ((uint32_t) kernel_uarg->uspace_stack) +
            kernel_uarg->uspace_stack_size;

        /* set where uspace execution starts */
        ustate.pc = (uintptr_t) kernel_uarg->uspace_entry;

        /* status register in user mode */
        ipl_t user_mode = current_status_reg_read() &
            (~STATUS_REG_MODE_MASK | USER_MODE);

        /* set user mode, set registers, jump */
        asm volatile (
            "mov sp, %[ustate]\n"
            "msr spsr_c, %[user_mode]\n"
            "ldmfd sp, {r0-r12, sp, lr}^\n"
            "nop\n"             /* Cannot access sp immediately after ldm(2) */
            "add sp, sp, #(15*4)\n"
            "ldmfd sp!, {pc}^\n"
            :: [ustate] "r" (&ustate), [user_mode] "r" (user_mode)
        );

        /* unreachable */
        while (true)
                ;
}

/** @}
 */